A liquid crystal display (LCD) device is commonly being used as a flat panel display device realizing high image quality and low power consumption. The LCD device displays an image by controlling an electric field applied to a liquid crystal cell and modulating light incident onto the liquid crystal cell. The LCD device includes a thin film transistor array substrate, a color filter substrate, or a liquid crystal layer interposed therebetween.
The LCD device is divided into a twisted nematic mode (TN mode) and an in-plane switching mode (IPS mode) according to a driving method of liquid crystal molecules.
The TN LCD device includes a thin film transistor array substrate including pixel electrodes, a color filter substrate, and a liquid crystal layer formed between the two substrates. The liquid crystal layer is driven by a vertical electric field between the common electrode and the pixel electrode. Here, the pixel electrode is formed in the thin film transistor array substrate in each unit pixel, and the common electrode is formed over the color filter substrate.
The IPS-LCD device includes a thin film transistor array including common electrodes and pixel electrodes, a color filter substrate including common electrodes, and a liquid crystal layer formed between the two substrates. The liquid crystal layer is driven by a parallel electric field parallel to the surface of the substrate between the common electrode and the pixel electrode. Here, the common electrode and the pixel electrode are alternately formed in each unit pixel at a certain interval therebetween.
In the IPS-LCD device constructed in such a manner, liquid crystal molecules within a liquid crystal layer are always switched on the same plane, so that the grey level is low in both vertical and horizontal viewing angles. For this reason, such an IPS-LCD device may improve viewing angle better than the TN-LCD device.
The switching time of the liquid crystal molecules (i.e., the time it takes for liquid crystal molecules to react to an electric field and the time it takes for liquid crystal molecules to return to an initial alignment state when the electric field is cut off) may be made to be short by reducing an interval (i.e., liquid crystal cell gap) between the thin film transistor array substrate and the color filter substrate or increasing a driving voltage.
However, reducing the liquid crystal cell gap is limited.
Also, when the driving voltage is increased, the time it takes for liquid crystal molecules to react to an electric filed may desirably decrease, but the increase in the driving voltage is limited by a driving IC and a power consumption. Also, such an increase in the driving voltage has no effect upon the time it takes for the liquid crystal molecules to return to an initial alignment state after an electric field is cut off.
Accordingly, according to the related art, it is limited to improve the drive time of liquid crystal molecules using the liquid crystal cell and the driving voltage.